The improved burner assembly of this invention is utilized in that capacity generally defined as a direct-fired gas industrial or related type of air heater. This type of heater is normally employed within an industrial complex, or a large space to be heated, and requiring large volumes of heated air to be added into the overall volumetric space to be heated, or to have heat supplementally added thereto, to attain an ambient temperature within the building that is comfortable for the purposes of its design. The invention herein is not a heat exchanger, since the combustion of the gas after its ignition takes place directly within the air stream being heated, and not by any conduction thereof. But, it is the improvement of the invention that further adds to the efficiency of combustion within an industrial heater of this design, so as to work most effectively, and safely, in producing the quantity of heated air that may be needed to warm the environs, and to effectively maintain a uniform and comfortable temperature within a predetermined volumetric space, as within a building, but at the same time, do so in a manner that does not sacrifice safety in heater design, during the performance of gaseous combustion in producing the source of heat. As a result, the heating equipment of this invention, in which the direct-fired burner of this type is enclosed, contains no flue, and all of the by-products of combustion are released directly into the heated air stream, which is then directly discharged into the space being heated, and as a result it is desirable, and one of the primary further advantages of this current invention, to provide improved means for reducing the creation and release of deleterious exhaust or other gases, either in the form of carbon monoxide, or nitrogen dioxide, that is discharged during the gas consumption. The improved heater of this design substantially reduces to a minimum the generation of these deleterious types of combustion by-products that may be directed into the space being heated, and certainly functions to alleviate the likelihood that any persons therein may be harmed through the breathing of such noxious gases over a sustained period of time.
Direct-fired gas heaters typically are constructed to a variety of configurations. In the majority of such heaters, as manufactured, the burner is arranged upstream of the fan inlet, and which functions in the manner of the draw-through type of arrangement. A number of other manufacturers position their burners downstream of the fan or blower discharge, in what is defined as a blow-through configuration. An example of the latter can best be seen in the U.S. Pat. No. 3,630,499, which is owned by a common assignee of the improved burner of this current design.
Other types of burner arrangements that exist in the prior art can be readily seen in the Ehrich U.S. Pat. No. 3,485,043; Coppin et al U.S. Pat. No. 4,573,907; in the Childs U.S. Pat. No. 3,993,449; in addition to the Pillard U.S. Pat. No. 3,885,919. Also, the Canadian patent No. 560,916, to Kind, shows a form of gas burner contained within a heating arrangement which incorporates a flame zone of a combustion chamber.
In addition, other burner assemblies are shown in the prior United States patents to Lewis, U.S. Pat. No. 4,523,905; the patent to Coppin, U.S. Pat. No. 4,869,665; and, Kikutani, et al U.S. Pat. No. 4,610,626.
As is well known in this art, the performance characteristics of the burner necessarily determines the operational range of the heating equipment, when tested, to guage whether it is in compliance with the various requirements of the American National Standards Institute (ANSI), governing the functioning of the direct gas-fired industrial air heaters, of the type described in accordance with this invention. The burner design for which patent protection is sought herein is utilized in the industrial heating appliance, such as the identified direct gas-fired make-up air heaters and direct gas-fired industrial air heaters. This design may also be utilized in industrial process equipment, such as ovens or dryers. These appliance standards that exist for this type of equipment, when it is utilized for providing tempered replacement air as in a make-up air application or for providing space heating to overcome the heat loss in industrial buildings, are regulated by standards, and two of such standards which are generally referenced by building code authorities are the ANSI standard Z-83.4, for the direct gas-fired make-up air heaters, and the ANSI standard Z-83.18, for the direct gas-fired industrial air heaters. These standards establish the criterian for the maximum increase allowed through the heater for the by-products of the combustion, such as the carbon monoxide, carbon dioxide, nitrogen dioxide, and aldehydes. Obviously, such controls are done for the purpose of regulating the air quality of the facility where the equipment is to be installed, for the safety of the worker, and others, subject to such type of heating conditions. Generally, the air flow through a heater of this type design, and the temperature rise that occurs for the air that is being heated, determines the heating capacity of the subject unit. The air flow is directly related to the fan as selected, the motor horse power of the unit driving the fan, and the static pressure on the system during its functioning. The temperature rise is controlled by the gas flow delivered to the burner, at the given air flow rate for the capacity of air that has been blown through the unit, as induced by the blower.
As previously explained, the ANSI standards generally provide an industrial self regulation of the minimum requirements that must be met by units of this design. These standards generally allow for specific maximum additive levels of four particular by-products of combustion, as previously identified, that may be released from the heating unit of this type during its functioning. These products of combustion, as previously explained, and their respective allowable levels are as follows:
carbon dioxide, 4,000 parts per million (ppm); PA1 carbon monoxide, 5 parts per million (ppm) PA1 nitrogen dioxide, 0.50 parts per million (ppm); and PA1 aliphatic aldehydes, 1.0 parts per million (ppm).
The allowable rise concentration through the heater for carbon monoxide is this 5 ppm, and for nitrogen dioxide is 0.5 ppm. As can be understood, these are extremely small levels of elevation, and therefore, it is very important that a burner of this design be very efficiently and effectively designed, for the purpose of minimizing the derivation of these combustion by-products. These particular derived deleterious chemcial compounds, which are generally recognized in the trade as undesirable by-products from the functioning of heating units of this type, and their gases of combustion, are basically recognized as unwanted derivatives, which, if they can be reduced to an absolute minimum, not only adds to the safety of all people within the heated space, but enhances the quality operations of the heating unit, as designed. The unit of this particular invention has been designed to provide for a minimization of the output of these undesirable compounds, through the unique enhanced design of particular characteristics and features constructed into the improved heater of this invention, to attain such desirable results.
It has previously been determined through testing that there are three major factors that effect the production of carbon monoxide within the gas combustion production process. Ideally, the gas and combustion air needs to be mixed as completely and thoroughly as possible as soon after the gas is introduced into the burner assembly. On the other hand, the quantity of air delivered must be at that level which induces effective controlled combustion, to provide maximum heat, without generating hot spots within the burner assembly, and more specifically its combustion chamber. If too little air is entered into the combustion chamber of the burner, then incomplete combustion occurs, and noxious gases can escape into the heated environment. This raises the level of carbon monoxide output, which could easily be measured in the discharge air stream. On the other hand, if too much combustion air is introduced at the low and medium fire combustion zone, quenching of the flame can occur, and this abrupt cooling also causes incomplete combustion. All this can produce the undesirable type of deleterious by-products, as previously explained. Thus, an equilibrium point desirably must be attained and maintained with respect to how much air is introduced into the burner, in combination with the amount of gas discharged from the manifold, and the location in emplacement of the air intake into the combustion zone.
An additional factor which effects the development of carbon monoxide in the burning process is also related to this quenching feature of the flame, but in this particular case, with respect to this heater, the concern is with the abrupt cooling of the flame after it exits from the burner. In units of this type, the discharge air leaving the fan or blower results in a greater volume of air being forced around the burner compared to that entering the combustion zone. With the burner downstream of the blower, the burner acts as a restriction to the flow of air, thereby compressing the air, causing the velocity to increase as it passes the burner. Once the restriction is passed, the large volume of air from the upper and lower portions of the duct expands rapidly to equalize pressure within the duct causing the cool air to impinge the flame tips that are extending beyond the end of the burner. This type of air impingement causes a quenching of the flame in prior art type of devices, and has significantly increased CO output.
The manner in which the air is introduced into the burner, as through arranged orifices, is a factor which is just as important as to how much air is introduced into the same. It has been found that the output level of carbon monoxide can readily be reduced limiting the amount of combustion air early in the burner, near the gas ports, and supplying more air later, or further downstream, within the burner assembly. This invention envisions the usage of diverter means to assure that a greater supply of the air is delivered downstream from the burner manifold, than that which enters into the combustion chamber just proximate its manifold. Thus, combustion takes place early in the burner at low combustion rates. With high combustion rates, as when an abundance of gas is introduced through the manifold, such combustion takes place more thoroughly throughout the whole burner assembly and more downstream from the intake gas manifold. Therefore, at lower combustion rates, less gas and less air will by necessity be needed to support such combustion. Also, at higher combustion rates, when more air is needed, it is preferably supplied more downstream in the burner assembly.
The current invention has been designed to take into consideration these various features, and to not only regulate the amount, capacity, and particularly location of the quantity of gas being ejected from the manifold into the chamber of combustion, but likewise, to provide for the adequate regulation in the delivery of air into the combustion chamber, the proper placement of its positioning, all within the area of combustion, and to inject the adequate amount of air to augment combustion, at particular locations, and to specific amounts, in order to enhance the efficiency of combustion, and thereby reduce the development of noxious gases released as exhaust from the heater assembly.
In addition to the foregoing, the subject matter of this invention further contemplates modifications to the structure of the burner embodiment, and more specifically its various formed chambers, in order to minimize the amount of heat exposure of the various walls and chambers, in addition to adding modifications, in the form of air balancing baffles, to select baffled tiers to better isolated areas of desired maximum combustion, to reduce the development of hot spots upon the various structured walls, and thereby, and which has been found through experimentation and research, to favorably reduce the development of nitrogen dioxide, and its emisions, from the burner of this invention during its functioning.